The invention relates to the field of documentation technology, particularly microfilm technology, and deals with an apparatus for the detection of optical marks on a film support which is moved relative to the detection apparatus.
In order to avoid space-intensive filing, the microfilming of documents has become widely used. Microfilmed documents take up little space, but on the other hand it is not possible to directly examine them. Two different functions are required to make them "recognizable", firstly, the recovery of a sought document from the compressed information space and, secondly, the conversion of the miniaturized optical image to physiologically correct dimensions for the human eye. In the prior art an attempt has always been made to simultaneously perform both functions with a single apparatus.
For recovery purposes, the individual information units (e.g. documents) are marked with optical marks which, when adequately detected, should lead to the sought document. The refound document is then generally projected in a manner suitable for reading and can be optionally directly reenlarged on paper. The invention deals with the first part of the problem, namely the seeking of the desired document, particularly on roll films, in which the information is filed sequentially or blockwise sequentially.
The optical marks on roll films, called image marks or blips, generally lead to the desired information by counting. In order to count the blips, they must be previously scanned and detected. It is here that an apparatus problem occurs. Blips are now conventionally detected by means of optical semiconductor sensors, e.g., by a phototransistor or a photodiode, which is either located in the direct vicinity of the film or, by means of an optical glass fiber, is coupled into the transmitted light path to measure the locally variable densities of the film. The sensor must coincide with the geometrical locus of the blip perpendicular to the direction of movement and therefore, due to the different positioning of the blips on the film, due to fluctuations in the image mark arrangement within the film or due to divergences in the image mark arrangements between individual films, etc. must be mechanically adjustable. By means of such a mechanical adjusting device, the sensor is adjusted to the blips which, as stated, apart from possible different positions on the film can also have different sizes, with possibly different information contents, in order to ensure a completely faultless scanning. However, it not infrequently occurs that during operation readjustment is necessary or the blip track is varied from roll to roll, which also requires an adjustment.
Thus, DE-OS No. 2256304 discloses a search reader with such a displaceable mounting support of the photoelectric cell, i.e. the photoactivatable element, in which readjustment is possible when required. However, this is contrary to the complete automation of a planned information search. The monitoring of the photoelectric cell function by humans is still necessary, apart from the monitoring of the documentation search, in the way in which it has always been necessary in a time-consuming manner, although human intelligence should only really be used for the evaluation of the document.